A. Field of the Invention
The present invention relates to lighting fixtures that produce high intensity, controlled, and concentrated light beams for use at relatively distant targets. In particular, the invention relates to such lighting fixtures, their methods of use, and their use in systems where a plurality of such fixtures are used in combination, usually elevated on poles, to compositely illuminate a target area energy-efficiently, with reduced glare and spill light. One primary example is illumination of a sports field.
B. Problems in the Art
Illumination of sports fields is generally called sports lighting. FIGS. 1A-1G illustrate one such sports lighting configuration. Football field 5 of FIG. 1A is illuminated by a set of arrays 1 of light fixtures 2 elevated on poles 6 (see FIG. 1A). As is well known in the art, there are known methods to design the number, type, and position of poles 6 and fixtures 2 to provide a desired or required amount and uniformity of light for the field. There are usually pre-designed lighting quantity and uniformity specifications to follow.
The most conventional form of sports lighting fixture 2 is a several feet in diameter bowl-shaped aluminum reflector with a transparent glass lens 3 suspended from a cross arm 7 fixed to a pole 6 by an adjustable knuckle 4 (see FIG. 1B). Each light fixture 2 has some adjustability both around vertical and horizontal axes. Each fixture 2 can therefore be uniquely aimed relative to the target area or field 5 by adjustment of knuckle 4 relative cross arm 7.
It is advantageous and efficient to use the cross-arms as reference points when mounting and aiming the fixtures. If the cross-arm can be assumed to be in a known orientation relative the target area once installed on a pole, the aiming of the fixtures can be a relatively simple process. A pre-determined angular orientation for each fixture relative to its cross-arm can be given to the installer. Sometimes gauges are integrated into the mounting knuckle and the installer simply sets the knuckle to the indicated aiming angle for that fixture. Sometimes the knuckle can even be factory configured to have one angular orientation to eliminate installer error.
While the above methods can save substantial time and labor over individual on-site fixture aiming, the assumption that the cross-arms will end up in the assumed orientation when installed on the poles can be erroneous. For example, this assumes the cross arm is orthogonal to the axis of the pole all along its length. Sometimes, during manufacturing, the surface to which the fixtures are mounted may be warped or other than in a common plane. The cross-arm can be slightly twisted around its longitudinal axis. If the surface is not in a common plane and orthogonal to the axis of the pole, even if the installer mounts the fixtures in their pre-determined angular orientation to the ground, they will not be correctly aimed. Because the fixtures are many times hundreds of feet from their intended target on the target area or field, a relatively small warpage (e.g. a few degrees from the assumed plane or less) could result in a substantial shift of the center of the beam on the field. This can result in non-uniformity in lighting at the field. It sometimes can result in light spilling outside the field.